The heart rate, or pulse rate, is the rate at which the heart beats. A normal heart rate for a healthy adult ranges from 60 to 100 beats per minute, reports the University of Virginia Health System. The heart's rhythm is controlled by electrical pulses produced in the natural pacemaker, known as the sinus node, located in the right atria (upper right chamber). When a condition, disease or outside stimulant interferes with the electrical system within the heart, the heart may respond by beating too fast. A heart rate that is significantly faster than normal is a condition known as tachycardia. Although some people who have a high heart rate experience no symptoms, others may feel dizziness, shortness of breath, lightheadedness or chest pain. A high heart rate interferes with the normal function of the heart, which can lead to dangerous effects.
A rapid heart rate can cause the heart to pump ineffectively. This means that the contractions of the heart muscle are so fast that blood remains in the lower chambers, or the ventricles. As blood sits in the lower chambers of the heart, it can form clots. A blood clot within the heart can block blood flow, resulting in a heart attack. If the clot is pumped out of the heart, it can travel through the arteries of the body. A blood clot that becomes stuck in an artery leading to the brain deprives the brain of blood and, therefore, oxygen, resulting in a stroke.
As the heart beats rapidly, less blood may be pumped to the body. In response, the heart tries to beat even faster to supply more blood and oxygen. Over time this causes greater and greater stress on the heart. When the heart is not able to pump blood as fast as the cells and organs in the body need it, heart failure can occur as described by the San Diego Cardiac Center sponsored website Heart Failure Online.
A high heart rate can make the pumping action of the heart ineffective. When the tissues of the body are deprived of oxygen, the patient may feel dizzy and lightheaded. If the brain does not receive adequate oxygen, fainting--also called syncope--may occur. Frequent fainting can be a danger. It is a sign that the brain is being seriously deprived of oxygen, which can lead to further complications, including brain damage and stroke.
There are several different types of tachycardia. Some originate in the atria, while others originate in the ventricles. In cases of ventricular tachycardia as well as in those of ventricular fibrillation, abnormal electrical impulses in the ventricles cause a high heart rate and interfere with the pumping of blood to the body. Both ventricular tachycardia and ventricular fibrillation are medical emergencies, according to doctors at the Mayo Clinic, as they can lead to sudden death if a normal heart rhythm is not restored.